FIGS. 1-6 to which it is now made reference schematically represent a multiformat film clamp of the type described in commonly assigned copending application Ser. No. 906,635 filed on Jun. 30, 1992, entitled "Multiformat Film Clamp" and filed in the name of Eastman Kodak Company.
Reference is now made to FIG. 1 in which is shown an embodiment of the film clamp in the open (unclamped) position.
In this embodiment, there is a base plate 2 which has a fixed mount 7 attached to it. The fixed mount 7 supports a platen or a main clamp frame 9, which is pivotally mounted by two pins 8. The main clamp frame 9 is manually opened and closed by holding the relieved outboard corners 20 which act as handles. It is to be appreciated that the frame 9 does not have to be pivotally mounted to the base plate 2, but could be freely positioned over the base plate 2 or guided with vertical guides into clamping alignment with the base plate 2.
Pivotally mounted to the inside opening of the main clamp frame 9 is a gimbal frame 11. Two pins 10 allow the gimbal frame 11 to rotate about an axis parallel to the main clamp frame 9's pivot axes, defined by pins 8 to provide a first degree of freedom.
Pivotally mounted to the gimbal frame 11 is an insert frame 13, which is pivotally mounted by two pins 12. The two pins 12 allow the insert frame 13 to rotate perpendicular to the main clamp frame 9's pivot axis to provide a second degree of freedom.
A clamp insert 14 having an aperture opening 5 is snapped into the insert frame 13 with a pair of ball plunger detents not shown. This allows the operator to quickly change the clamp insert 14 for different formats.
Likewise, an aperture plate 3 is held in place via magnets (not shown) which are mounted slightly below the top surface of base 2.
The gimbal frame 11 provides for self aligning of the clamp insert 14 (an insert for 35 mm film is shown in FIG. 1) to the surface of the aperture plate 3, when the clamp frame 9 is rotated to the close position (as shown in FIG. 2).
The film 1 is located along its width by four positioning pins 4 which are fixed to the aperture plate 3. There are different size aperture plates and pin positions for different film formats. FIG. 3 illustrates an aperture plate 3 having an aperture opening 5 defined therein with positioning pins 4.
FIG. 4 illustrates the clamp insert 14 having two pairs of outwardly angled flexible strips 25, such as rubber, fixed about its aperture opening 5. The rubber strips are at equal heights above the clamp inserts top surface. Although the rubber strips 25 are shown fixed to the clamp insert they may alternately be affixed to the aperture plate or to both the aperture plate and to the clamp insert. Openings 21 are provided in the clamp insert for receiving the positioning pins 4 when the clamp is closed.
Typically, in such a film clamp, said rubber strips 25 are comprised of a flat strip (FIG. 7) with an angle (typically 60.degree.) on one surface 26. As shown in FIG. 4, said pair of rubber strips 25 are contained in four locating slots 21, 22, 23, and 24 located all around the aperture opening 5, said slots being slanted (typically 60.degree.) with respect to the normal to the surface of the clamp insert, so that when the rubber strips 25 are inserted into said slots 21, 22, 23, and 24, each of said strips is angled outward from the aperture opening 5 so as to grip and tension a film positioned between said base plate and said platen when they are clamped together.
During clamping of the film strip 1 the rubber strips 25 compress and buckle outward from the center of the apertured opening 5 to provide the clamping and tensioning forces as illustrated in FIGS. 5 and 6 to the film 1.
Referring to FIG. 5, the film 1 is clamped and tensioned along the width and length edges of film area.
FIG. 6 illustrates that all edges of the film 1 are under the same clamping force F.sub.2 sin .theta. and same tensioning force F.sub.2 cos .theta.. The force resistive to the motion of the film 1 at all edges is .mu.F2 sin .theta..
Note that, .mu. is the coefficient of friction between the film 1 and surface of the aperture plate 3. To function properly the following relation must be maintained: EQU F.sub.2 cos .theta.&gt;.mu.F.sub.2 sin .theta.
This allows the film 1 to move relative to the platen surface, but not relative to the tensioning clamp.
The clamping force is generated by rotating a cam knob 6 180.degree. to the clamp position, similar to a window latch. The cam knob is pivotally mounted to the base 2 by a pivot shoulder screw 18, as seen in FIG. 2.
For convenience, film strip guides 17 are attached to each side of the base 2 to facilitate the holding of film strips by their edges.
Finally, both the gimbal frame 11 and insert frame 13 rotation can be limited by pins 19A and associated clearance holes 19B as illustrated in FIG. 1.
Such a film clamp, even if it provides a uniform clamping and tensioning form around the perimeter of the filing, exhibits some drawbacks. First of all, the slanted slots, either in the aperture plate, or in the clamp insert, or both cause some loss in the viewable area of film which is substantially reduced due to the angle formed by said locating slots. Then, with such a design of the rubber strips, any functional changes required for further development or optimization for holding untested media, mandate the manufacture of new clamp inserts with modified slot dimensions. Furthermore, the angled locating slots 21, 22, 23, and 24 are complex and expensive to machine, the depth of said angled slots requiring to be closely controlled so that said rubber strips can provide a uniform clamping and tensioning force around the perimeter of the film.